Human T-cell lymphotropic virus types 1 and 2.

Human T-cell lymphotropic virus types 1 and 2 (HTLV-1 and HTLV-2, respectively) are part of the Retroviridae family and members of the Deltaretrovirus genus. However, high-risk populations, such as intravenous drug users (IDUs), in which HTLV-2 infection predominates over HTLV-1 infection, are reported to have a seroprevalence of up to 20%. IDU and sex with IDUs are the most important risk factors for HTLV-2 transmission. Peripheral blood mononuclear cells (PBMCs) are appropriate specimens for nucleic acid detection and virus isolation since HTLV-1 and HTLV-2 are cell-associated viruses. Two qualitative PCR procedures, utilizing primers in the pol or tax gene region, have been used to confirm and differentiate between HTLV-1 and HTLV-2 infections. The first uses HTLV consensus primers that allow amplification of both viruses; typing is achieved either by hybridizing the product to an HTLV-1-specific or HTLV-2-specific probe or by specific restriction digestion pattern analysis. The second approach employs type-specific primers and probes in separate amplifications. Testing for antibodies to HTLV-1 and HTLV-2 should be performed for all blood donors and any patients presenting with relevant clinical signs and symptoms. A typical algorithm for HTLV testing for diagnostic purposes is outlined in this chapter. If the initial screening immunoassay (EIA or ChLIA) is reactive, a repeat assay of the same specimen is performed in duplicate.